1. Field of the Invention
The present invention relates to a transflective liquid crystal display device having a transmissive region transmitting backlight and a reflective region reflecting ambient light that are formed in pixel region.
2. Description of the Background Art
A transflective liquid crystal display device has a TFT (Thin Film Transistor) array substrate. On the array substrate, each pixel has a transmissive region that transmits backlight emitted from the rear side of the display surface and a reflective region that reflects ambient light coming into the liquid crystal layer.
In a conventional technique for transflective liquid crystal display devices thus structured, reflective electrodes in the reflective regions, source bus lines (including source electrodes), and drain electrodes are formed in the same layer (see Japanese Patent Application No. 2004-110299, which is hereinafter referred to as Patent Document 1). Application of the technique of Patent Document 1 simplifies the manufacturing process.
The transflective liquid crystal display device according to the Patent Document 1 requires preventing short-circuits between the source bus lines and reflective electrodes. Accordingly, the source bus lines and reflective electrodes, formed in the same layer, are separated away from each other by given spaces (distances).
In the transflective liquid crystal display device of the Patent Document 1, a storage capacitance electrode and storage capacitance bus line exist under the interval between a source bus line and a reflective electrode. Thus, in the transflective liquid crystal display device, the storage capacitance electrode and storage capacitance bus line face the opposing electrode provided on the opposing substrate placed opposite the TFT array substrate.
In the transflective liquid crystal display device of Patent Document 1, the storage capacitance electrode and storage capacitance bus line are at the same potential as the opposing electrode. Accordingly, no electric field is applied to the liquid crystal layer above the interval (the given space (distance)) between the source bus line and the reflective electrode. Then, it is not possible to control, with an electric field, the light entering the display area and reflected at the storage capacitance electrode and the like existing under that interval.
Accordingly, when the transflective liquid crystal display device of the Patent Document 1 adopts a normally white mode (a mode which displays white when no voltage is applied), the reflectivity is increased in display of black because the reflected light cannot be controlled with an electric field, which leads to reduction of reflective contrast.
Japanese Patent Application No. 2004-260873 (hereinafter referred to as Patent Document 2) discloses a transflective liquid crystal display device that solves this problem.
According to the technique of Patent Document 2, a reflective contrast reduction preventing electrode is formed in order to allow application of an electric field to the liquid crystal layer above the interval between the source bus line and the reflective electrode. Accordingly, the transflective liquid crystal display device of Patent Document 2 prevents the reduction of reflective contrast.
Now, the reflective contrast reduction preventing electrode is electrically connected with a transmissive pixel electrode formed in the transmissive region.
In the transflective liquid crystal display device of the Patent Document 2, when conductive foreign matter enters between the reflective contrast reduction preventing electrode and the opposing electrode, or when the opposing electrode is deformed during manufacturing process, for example, the opposing electrode and the reflective contrast reduction preventing electrode may be short-circuited.
Then, because the reflective contrast reduction preventing electrode is electrically connected to the transmissive pixel electrode as mentioned above, the transmissive pixel electrode and the opposing electrode may be electrically short-circuited as a result (hereinafter a short-circuit of this kind is referred to as an inter-surface short-circuit).
If an inter-surface short-circuit occurs, no electric field is applied to the liquid crystal layer in the area corresponding to the short-circuited portion. In a normally white mode device, the absence of electric field application to the liquid crystal layer in a transmissive region allows the backlight to come out through the display area. The backlight coming out through the display area results in a very noticeable defect called “a bright dot defect”.
In addition, in the transflective liquid crystal display device of the Patent Document 2, the reflective contrast reduction preventing electrode must be formed in the reflective region near a border between pixels. However, in general, the cell gap is narrow in the area where the reflective contrast reduction preventing electrode is formed. Therefore, the transflective liquid crystal display device of the Patent Document 2 is susceptible to inter-surface short-circuiting caused by contamination by foreign matter.
Furthermore, the reflective contrast reduction preventing electrode is formed near a border of the color filter pattern formed on the opposing substrate. Accordingly, the transflective liquid crystal display device of Patent Document 2 is susceptible also to inter-surface short-circuiting caused by abnormalities of the color filter pattern (abnormalities of the color filter pattern cause deformation of the opposing electrode).
That is, the transflective liquid crystal display device of Patent Document 2 is prone to bright dot defects because of the positioning of the reflective contrast reduction preventing electrodes, which leads to reduction of yield and hence to increased manufacturing costs.